1. Field of the Invention
This invention relates to a system and apparatus for the continuous surface treatment of a strip or web-like product, i.e. surface treatment particularly, but not exclusively, of a ferrous hot rolled strip in a processing line. More particularly, it relates to a sealed system comprising a plurality of cells, wherein the treatment fluid, such as hydrochloric acid or pickling liquor, is introduced at various locations to both the top and bottom of the product in each cell and is restricted in a space along the product and retained in the cell such that the treatment rate is significantly increased.
2. Description of the Prior Art
Conventionally, in the manufacture of ferrous articles, such as rolled metal strip, the article is taken through several treatment processing lines in the mill in order to produce a high quality product. These processes include pickling, cleaning, plating, coating, and/or other chemical treatment of the article. A demand for an increase in productivity in the recent years has required higher operating speeds of the processing lines, resulting in an increase both in the length of the line and in the operating and equipment costs.
Normally, the first step in finishing hot rolled ferrous strip is a descaling or pickling process, and then a rinsing of the metal strip, whereby in the pickling process the oxides and scales are chemically removed from both the top and bottom surfaces of the strip. It has become the general practice to pull strip by motor driven bridle rollers or by a tension bridle in a catenary fashion under a controlled speed through a series of three or four open troughs or tanks each typically measuring eighty to a hundred feet in length. These long, open tanks which usually have removable covers and are operated at slightly less than atmospheric pressure not only limit the speed in which the strip can travel in order to maintain the catenary condition and limit the tempratures at which pickling can be conducted without causing excessive evaporation losses of both water and acid, but they are relatively placid baths which tend to retard the chemical action because of relatively stagnant conditions of the pickling liquor near the strip surfaces.
To obviate evaporation and other losses, to conserve heat and pickling solution, and to accelerate the surface treatment process, the opened trough systems have been replaced with closed systems in the forms of troughs, chambers, tubes, and cells.
U.S. Pat. No. 1,837,159 discloses an elongated closed tube for pickling a moving strip whose edges are supported along the walls, thus minimizing friction upon the travel of the strip and permitting a substantial portion of the strip to be acted upon by the pickling solution.
U.S. Pat. No. 3,032,890 discloses a series of chambers including a central treating chamber for a strip or web and adjacent inlet and outlet chambers which evacuate the atmospheric gases so that treatment of the strip can more efficiently occur in the central treating chamber. The inlet and outlet chambers have a sealing structure comprising a pair of rollers for contacting the strip, and sealing plates of low friction material held in the housing of the sealing structure.
At the peripheries of the rollers the gas is caused to flow rapidly through the restricted orifices after which the gas is caused to enter a pocket where the gas expands and looses velocity.
U.S. Pat. No. 3,048,503 discloses recirculating pickling liquor to a sealed pickling chamber having air tube sealing means. U.S. Pat. No. 2,264,885 discloses a strip treating apparatus including plural pickling chambers each having circulating pickling liquor. In U.S. Pat. No. 2,234,815, a continuous strip pickling and cleaning apparatus is disclosed consisting of a pickling trough made up of multiple sections or modules. Several treatment chambers are combined in British Pat. No. 1,143,224 to form a continuous treatment line for the continuous surface treatment of strip and other simple shape objects. Pairs of rollers are arranged at the beginning and end of the line, as well as between the various chambers in order to convey the strip through the line.
The closed surface treatment systems of the sort mentioned above may to some extent minimize the evaporation losses of the solution; however, many fail in permitting an increase in the speed of the strip through the line, and most importantly, fail to uniformly treat the surfaces and to increase the speed or rate at which the treatment occurs upon the surface of the strip in its travel, all of which neglect to provide an optimum efficiency and productivity for the processing line.